Method of implanting an artificial disc replacement device

ABSTRACT

A method of implanting an artificial disc replacement device may include removing a natural spinal disc from between vertebrae, thereby forming a disc space between the first vertebra and the second vertebra and inserting a first endplate and a second endplate of the artificial disc replacement device into the disc space. Further, the method may include using a distraction tool to distract the first endplate and the second endplate in order to seat the first endplate against the first vertebrae and to seat the second endplate against the second vertebrae and performing an x-ray to evaluate the placement of the first endplate and the second endplate within the disc space. The method may include using the distraction tool to unseat the first endplate from the first vertebra and to unseat the second endplate from the second vertebra and repositioning the first endplate or the second endplate within the disc space.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. provisional application No. 62/964,956, filed Jan. 23, 2020, and entitled “Method of Implanting an Artificial Disc Replacement Device,” the entire disclosure of which is incorporated herein by reference.

BACKGROUND

The embodiments are generally directed to methods and devices for implantation in the spine, and in particular to methods of implanting artificial disc replacement devices.

An artificial disc, also known as artificial disc replacement (ADR), is a medical device implanted into the spine that acts as, or imitates, a spinal disc. Surgeons can replace the entire disc or remove only the nucleus (center of the disc). ADR devices may be designed to allow for motion between the adjacent vertebrae, rather than fuse adjacent vertebrae together as occurs in other kinds of spinal implants.

Current ADR systems may impede normal movement in the back and/or neck. For example, some systems allow vertebrae to pivot around a fixed central point but prevent the vertebrae from translating during flexion. Other ADR systems include a mobile core that can slide along one or both endplates. These mobile cores may become displaced from their intended range of motion, or their range of motion may be affected by scarring of the adjacent tissue, which may result in failure of the ADR and/or a limited range of motion. Also, in current ADR systems, the upper and lower endplates may come into contact during flexion and/or extension, thereby requiring the use of high strength materials such as metals. The use of metallic endplates may create unwanted visual artifacts during magnetic resonance imaging (MRI) of the patient's spine. These MRI artifacts may make it difficult for a radiologist and/or surgeon to accurately assess the state of the spine or surrounding tissue.

In addition, there are issues with the implantation processes for current ADR systems. Generally, current ADR devices cannot easily be test fit prior to permanent implantation. Because of this limitation, the devices may be misaligned or otherwise poorly positioned within the spine, which can lead to various problems. Inserting an ADR device too far can impinge upon the spinal cord. Inserting it not far enough and it can block motion or articulation of the spine. Insert the device too far to one side laterally and the spine can be placed into an unnatural bend. For example, in the cervical region, a laterally displaced implant can leave the patient with a tilted head at rest.

Current ADR devices are typically tapped in with a mallet or the like. This, in and of itself, requires exceptional precision because the implants are tapped in the direction of the spinal cord. Also, some ADR devices have a keel or rows of teeth that cut through the vertebral endplates as the implant is tapped into place. These keels or teeth create significant scoring in the vertebral endplates. Accordingly, if the device needs to be removed for repositioning, the vertebral endplates are left with significant gouges that will make it difficult to reinsert the device in any other position. In addition, with the teeth and keels set, it is not typically possible to remove the device without damaging the device itself.

Further, some ADR systems utilize a bulky jig for preparing the disc space. However, such jigs are so bulky and cumbersome that x-rays cannot be taken with the jigs in place.

There is a need in the art for a system and method that addresses the shortcomings discussed above.

SUMMARY

In one aspect, the present disclosure is directed to a method of implanting an artificial disc replacement device. The method may include removing a natural spinal disc from between a first vertebra and a second vertebra, thereby forming a disc space between the first vertebra and the second vertebra. The method may also include inserting a first endplate and a second endplate of the artificial disc replacement device into the disc space. Further, the method may include using a distraction tool to distract the first endplate and the second endplate in order to seat the first endplate against the first vertebrae and to seat the second endplate against the second vertebrae. Also, the method may include performing an x-ray to evaluate the placement of the first endplate and the second endplate within the disc space. In addition, the method may include using the distraction tool to unseat the first endplate from the first vertebra and to unseat the second endplate from the second vertebra and repositioning the first endplate or the second endplate within the disc space.

In another aspect, the present disclosure is directed to a method of implanting an artificial disc replacement device, including inserting a first endplate and a second endplate of the artificial disc replacement device into a disc space between a first vertebra and a second vertebra and using a distraction tool to distract the first endplate and the second endplate, thereby placing the first endplate against the first vertebra and placing the second endplate against the second vertebra. In addition, the method may include performing an x-ray to evaluate the placement of the first endplate and the second endplate within the disc space and using the distraction tool to reposition at least one of the first endplate and the second endplate within the disc space.

In another aspect, the present disclosure is directed to a method of implanting an artificial disc replacement device, including inserting a first endplate and a second endplate of the artificial disc replacement device into a disc space between a first vertebra and a second vertebra and using a distraction tool to distract the first endplate and the second endplate, thereby placing the first endplate against the first vertebra and placing the second endplate against the second vertebra. The method may also include using the distraction tool to reposition at least one of the first endplate and the second endplate within the disc space and inserting a core assembly of the artificial disc replacement device between the first endplate and the second endplate.

Other systems, methods, features and advantages of the embodiments will be, or will become, apparent to one of ordinary skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features and advantages be included within this description and this summary, be within the scope of the embodiments, and be protected by the following claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments can be better understood with reference to the following drawings and description. The components in the figures are not necessarily to scale, with emphasis instead being placed upon illustrating the principles of the embodiments. Moreover, in the figures, like reference numerals designate corresponding parts throughout the different views.

FIG. 1 is a schematic view of a portion of the cervical spine including an artificial disc replacement device disposed between two adjacent cervical vertebrae, according to an embodiment;

FIG. 2 is a schematic cross-sectional view of the artificial disc replacement device of FIG. 1 including the two adjacent vertebrae;

FIG. 3 is a schematic perspective view of the artificial disc replacement device of FIG. 1 ;

FIG. 4 is a schematic exploded view of the artificial disc replacement device of FIG. 3 ;

FIG. 5 is a schematic front view of a core assembly including a core member and a matrix member, according to an embodiment;

FIG. 6 is a schematic front view of the core assembly of FIG. 5 , in which the matrix member deforms under compressive forces;

FIG. 7 is a side schematic view of a core member of an artificial disc replacement device in which the variable curvature of the upward engaging surface in the longitudinal direction is visible, according to an embodiment;

FIG. 8 is a schematic front view of the core member of FIG. 7 in which the constant curvature of the upward engaging surface in the lateral direction is visible;

FIG. 9 is a schematic top-down view of an embodiment of a core member having a variable width;

FIG. 10 is a schematic side view of a patient looking forward with an enlarged view of an artificial disc replacement device in a neutral position, according to an embodiment;

FIG. 11 is a schematic view of the patient of FIG. 10 in which their neck is undergoing extension with an enlarged view of a corresponding configuration of the artificial disc replacement device;

FIG. 12 is a schematic view of the patient of FIG. 10 in which their neck is undergoing flexion with an enlarged view of a corresponding configuration of the artificial disc replacement device;

FIG. 13 is a schematic view of the patient of FIG. 10 in which their neck is undergoing further flexion with an enlarged view of a corresponding configuration of the artificial disc replacement device;

FIG. 14 is a schematic front view of a patient looking forward with an enlarged view of an artificial disc replacement device in a neutral position, according to an embodiment;

FIG. 15 is a schematic view of the patient of FIG. 14 in which their neck is undergoing lateral bending with an enlarged view of a corresponding configuration of the artificial disc replacement device;

FIG. 16 is a schematic view of an endplate of an artificial disc replacement device with a centrally located dome for engaging a recess in an adjacent vertebra, according to an embodiment;

FIG. 17 is a schematic view of an endplate of an artificial disc replacement device with a posteriorly located dome for engaging a recess in an adjacent vertebra, according to an embodiment;

FIG. 18 is a schematic view of an endplate of an artificial disc replacement device with a relatively flat dome for engaging a corresponding flat recess in an adjacent vertebra, according to an embodiment;

FIG. 19 is a schematic view of another embodiment of a core assembly and a lower endplate, in which a matrix member of the core assembly covers an entirety of the lower endplate;

FIG. 20 is a schematic perspective lateral view of a portion of a spine and two endplates of an artificial disc replacement device being inserted into the disc space between two vertebrae;

FIG. 21 is a schematic view of the spine shown in FIG. 20 with the device endplates inserted into the disc space;

FIG. 22 is a schematic view of the spine shown in FIG. 20 with the device endplates being distracted by a distraction tool;

FIG. 23 is a schematic view of the spine shown in FIG. 20 with the endplates seated and the patient undergoing an x-ray;

FIG. 24 is a schematic view of the spine shown in FIG. 20 with the endplates being withdrawn from the disc space;

FIG. 25 is a schematic view of the spine shown in FIG. 20 with the endplates being repositioned within the disc space;

FIG. 26 is a schematic view of the spine shown in FIG. 20 with the endplates once again being distracted;

FIG. 27 is a schematic view of the spine shown in FIG. 20 with the endplates distracted and an implant core assembly being inserted between the endplates;

FIG. 28 is a schematic view of the spine shown in FIG. 20 with the core assembly positioned between the endplates;

FIG. 29 is a schematic view of the spine shown in FIG. 20 with the distraction removed and the spine allowed to return into compression;

FIG. 30 is a schematic side view of a spine with endplates of an artificial disc replacement device being inserted between vertebrae of the spine;

FIG. 31 is a schematic side view of the spine shown in FIG. 30 with the endplates being distracted by a distraction tool;

FIG. 32 is a schematic side view of the spine shown in FIG. 30 with the endplates distracted and an implant core assembly being inserted between the endplates;

FIG. 33 is a schematic side view of the spine shown in FIG. 30 with the distraction removed and the spine allowed to return into compression; and

FIG. 34 is a flowchart illustrating steps of a method of implanting an artificial disc replacement device according to an embodiment.

DETAILED DESCRIPTION

The embodiments provide a spinal implant in the form of an artificial disc replacement device, also referred to simply as an ADR device. The ADR device can be implanted between adjacent vertebrae in the spine in order to replace damaged spinal discs. The exemplary ADR device is configured with an upper endplate and a lower endplate that sandwich a core assembly. The core assembly includes a core member that is partially embedded within a matrix member. The core member has a convex upward engaging surface. The upward engaging surface varies in curvature along a sagittal plane to facilitate natural motion between the adjacent vertebrae during flexion and extension. Specifically, the posterior portion of the core member has a smaller arc radius (and correspondingly, a larger curvature) than the anterior portion of the core member. This helps limit compression during extension and increases compression and forward translation of the upper endplate during flexion. The upward engaging surface has an approximately constant curvature along a coronal plane to facilitate symmetric lateral bending in either lateral direction.

The exemplary device also uses a matrix member that is less rigid than the core member, thereby improving cushioning and shock absorption. The matrix member may also extend upward from the lower endplate to engage the upper endplate during flexion and extension, thereby preventing the endplates from contacting one another. As the endplates never contact one another they can be constructed from materials other than metal. For example, the endplates may be constructed of ceramic or carbon materials that provide better biocompatibility with vertebra, improved wear characteristics and different degrees of strength compared to metal materials. Additionally, using ceramic or carbon materials may limit or eliminate MRI artifacts that can be caused by using metallic endplates.

FIG. 1 is a schematic view of an embodiment of an implant in the form of an artificial disc replacement device 100, also referred to simply as ADR device 100. In FIG. 1 , ADR device 100 is embedded within a portion 102 of a spinal column. Specifically, ADR device 100 is disposed between a first vertebra 110 and a second vertebra 112.

It may be appreciated that the ADR device described in this detailed description and in the claims may be used within any suitable portion of the spine. The embodiment of FIG. 1 depicts ADR device 100 used with lumbar vertebrae. However, other embodiments could include a device that may be used to replace spinal discs in any portion of the spine including the lumbar spine, the thoracic spine, and the cervical spine. For example, the embodiments described below and shown in FIGS. 10-15 depict an ADR device that is implanted between adjacent cervical vertebrae in the neck. It may be appreciated that suitable adjustments could be made to the dimensions and/or geometries of various parts of the ADR device in order to accommodate anatomic differences in the different regions of the spine.

For purposes of clarity, reference is made to various directional adjectives throughout the detailed description and in the claims. As used herein, the term “anterior” refers to a side or portion of an implant that is intended to be oriented towards, or disposed closer to, the front of the human body when the implant has been placed in the body. Likewise, the term “posterior” refers to a side or portion of an implant that is intended to be oriented towards, or disposed closer to, the back of the human body following implantation. Moreover, the posterior side and the anterior side of a body (or part) may be separated by a coronal plane (also known as a frontal plane).

In addition, the term “superior” refers to a side or portion of an implant that is intended to be oriented towards a top (e.g., the head) of the body while “inferior” refers to a side or portion of an implant that is intended to be oriented towards a bottom of the body. Moreover, the superior side and inferior side of the body may be separated by a transverse plane.

Reference is also made herein to “lateral” sides or portions of an implant, which are sides or portions facing along a lateral direction of the body. These lateral sides may be separated by a sagittal plane.

FIG. 2 is a schematic cross-sectional view of ADR device 100 as it is embedded within portion 102 of the spinal column. ADR device 100 is also shown in isolation in FIG. 3 . Additionally, FIG. 4 depicts an exploded isometric view of ADR device 100.

Referring to FIGS. 2-4 , ADR device 100 includes a first endplate 220 and a second endplate 230. First endplate 220, which may also be referred to as an upper endplate, is disposed on a superior side of ADR device 100. Second endplate 230, which may also be referred to as a lower endplate, is disposed on an inferior side of ADR device 100.

First endplate 220 may be configured to engage a first vertebra (for example, first vertebra 110 of FIG. 2 ). In some embodiments, first endplate 220 may include a dome 222 that can be fit into a corresponding recess (or concave area) within first vertebra 210. Dome 222 comprises a protrusion that helps align and hold first endplate 220 in position with respect to first vertebra 110. In particular, dome 222 may help keep first endplate 220 from translating laterally with respect to first vertebra 110.

Second endplate 230 may be configured to engage a second vertebra (for example, second vertebra 112 of FIG. 2 ). In some embodiments, second endplate 230 may include provisions for permanently attaching to a vertebra. In the exemplary embodiment, second endplate 230 includes a set of teeth 232 that can engage a vertebra.

Although the embodiments depict endplates with domes and/or teeth for engaging vertebrae, in other embodiments any other suitable provisions for attaching endplates to vertebrae could be used. Exemplary mechanisms include, but are not limited to: screws, rods, nails, and blades. In such embodiments, the endplates may be suitably modified to receive at least part of the fastening mechanism. For example, an endplate could include holes for receiving screws.

ADR device 100 may also include a core assembly 250 that is disposed between first endplate 220 and second endplate 230. Core assembly 250 of ADR device 100 may itself comprise two distinct members. Specifically, core assembly 250 comprises a core member 252 and a matrix member 254. Core member 252 further includes a base portion 260 and a curved engaging surface 262. As shown in FIG. 2 , base portion 260 of core member 252 may be embedded within matrix member 254.

First endplate 220 may include a recess 224 that receives curved engaging surface 262 of core member 252. As described in further detail below, recess 224 may be sized and shaped to receive different portions of curved engaging surface 262, allowing first endplate 220 to tilt and translate along curved engaging surface 262 so as to facilitate natural motions between adjacent vertebra during flexion, extension, and lateral bending. In the exemplary embodiment shown in FIG. 2 , recess 224 extends from an inferior side of first endplate 220 towards a superior side of first endplate 220. However, recess 224 does not extend into the portion of first endplate 220 defined by dome 222. In other embodiments, however, recess 224 could extend into the portion of first endplate 220 defined by dome 222, which may enable the overall thickness of first endplate 220 to be further reduced and/or the depth of recess 224 to be increased.

Second endplate 230 may include a recess 234 that receives matrix member 254. Recess 234 may be bounded by an outer wall or lip 235. In some embodiments, recess 234 is sized and dimensioned to tightly fit matrix member 254 so that, once inserted, matrix member 254 cannot be easily dislodged from recess 234. However, in other embodiments, matrix member 254 can be fixed within recess 234 using a suitable fastener and/or biocompatible adhesive.

Vertebral bodies are comprised of two distinct types of tissue: cortical bone and cancellous bone. The cancellous bone is disposed more centrally within the vertebral body, which is surrounded by an outer layer of cortical bone. At the superior and inferior ends of the vertebral body, the cortical bone forms a raised lip (or cortical rim) around the cancellous bone. Because the rim of cortical bone is denser and generally stronger than the interior cancellous bone, the endplates of the present embodiments are shaped to increase engagement with the cortical rim. Specifically, first endplate 220 and second endplate 230 both have approximately rectangular shapes with rounded corners. This geometry helps ensure that the endplates are supported, at least in part, by the cortical rim of each vertebral body.

Although the embodiments depict endplates with an approximately rectangular geometry, in other embodiments the outer perimeter of each endplate may be varied to approximately match the geometry of the cortical rim of the associated vertebral body. Thus, in some cases, endplates could have a curved front edge that matches the approximate geometry of the anterior lip of the associated vertebral body. Likewise, in some cases, endplates could have lateral and/or posterior edges that match the approximate geometries of the lateral and/or posterior portions of the cortical rim.

FIG. 5 is a schematic view of core assembly 250 shown in isolation. As seen in FIG. 5 , base portion 260 may be embedded in matrix member 254. That is, base portion 260 may be surrounded from an inferior (lower) side, as well as from the lateral sides, by portions of matrix member 254. However, matrix member 254 does not cover or encase a substantial portion of curved engaging surface 262, which extends out from a superior surface 502 of matrix member 254. With this configuration, curved engaging surface 262 directly engages first endplate 220 (see FIG. 2 ), while preventing any portion of core member 252 from coming into direct contact with second endplate 230.

Core member 252 and matrix member 254 may be made of substantially different materials. In some embodiments, core member 252 may be made of a more rigid material than matrix member 254. Also, matrix member 254 may be made of a substantially more compressible material than core member 252. For example, as seen in FIG. 6 , matrix member 254 may undergo substantial compression in a vertical direction under vertical loads 602. By contrast, core member 252 may not compress substantially under these same loads. As seen by comparing FIGS. 5 and 6 , the vertical thickness of matrix member 254 may compress from a first thickness 520 to a second thickness 620 while core member 252 maintains a substantially constant thickness 522 before and during compression.

Embedding part of core member 252 within a more flexible and/or compressible matrix material allows for cushioning and shock absorption within ADR device 100. Furthermore, this configuration allows core member 252 to “float” within matrix member 254, thereby providing some relative movement between core member 252 and second endplate 230 (see FIG. 2 ). Moreover, because matrix member 254 separates core member 252 and second endplate 230, there are no frictional or other contact forces generated between these two components as they move relative to one another. This may reduce the likelihood of mechanical failure. As described in further detail below, matrix member 254 may also provide a cushion that prevents the opposing endplates from coming into contact with one another during flexion or extension. This eliminates contact forces between the endplates and allows for the use of a wider range of non-metallic materials for the endplates. Additionally, by using a flexible and/or compressible matrix member, the present embodiments facilitate vertical cushioning during compression. That is, the vertical displacement between the upper and lower endplates at one end may be decreased, in part, by the vertical compression of the matrix member. This facilitates compression of the spine along the anterior side during flexion while also providing shock absorption.

In different embodiments, a variety of suitable materials could be used for the components of an ADR device. Suitable materials for a core member include, but are not limited to: metallic materials, plastic materials, and/or ceramic materials. Suitable materials for a matrix member include, but are not limited to: plastics and gels. Suitable materials for endplates include, but are not limited to: metallic materials, plastics, and/or ceramics. In one exemplary embodiment, a core member could be comprised of a polyether ether ketone (PEEK) material. Also, in one embodiment, a matrix member could be comprised of a suitably flexible gel. Additionally, in one embodiment, one or both endplates could be comprised of a suitable ceramic material.

The embodiments provide an artificial disc replacement that facilitates natural motion between vertebrae. This is accomplished, in part, by the geometry of the core member, which has a curvature that varies over different regions. In particular, the curvature may vary between the posterior and anterior sides of the core member. That is, the radius of curvature changes from the posterior end to the anterior end.

FIG. 7 is a schematic side view of core member 252. Visible within FIG. 7 is a sagittal plane 702 and a coronal plane 704 (shown here as a line). Coronal plane 704 divides core member 252 into a posterior side and an anterior side. Core member 252 further includes a posterior portion 710 associated with its posterior side and an anterior portion 712 associated with its anterior side.

The posterior and anterior portions may be associated with different degrees of curvature. In this description and in the claims, the curvature of a surface may be characterized by its radius of curvature, or arc radius. The arc radius of an arc, for example, is the radius of the circle of which the arc is a part. Moreover, the curvature of a local portion of a surface is inversely proportional to the associated arc radius of that local portion. In particular, a larger arc radius is associated with a smaller degree of curvature, while a smaller arc radius is associated with a larger degree of curvature.

As seen in FIG. 7 , curved engaging surface 262 includes a curved boundary 720 that lies within sagittal plane 702. Curved boundary 720 has a curvature that varies along its length. Specifically, along posterior portion 710, curved boundary 720 has a first arc radius 730. Likewise, along anterior portion 712, curved boundary 720 has a second arc radius 732. As shown schematically in FIG. 7 , first arc radius 730 is substantially smaller than second arc radius 732. This corresponds to a greater curvature for posterior portion 710 than for anterior portion 712.

In some embodiments, the arc radius of curved boundary 720 may gradually change between first arc radius 730 to second arc radius 732. This may occur within a transition portion 740 that is intermediate to posterior portion 710 and anterior portion 712. In some cases, the arc radius could vary smoothly from first arc radius 730 to second arc radius 732. In other cases, however, the arc radius could abruptly change.

In different embodiments, the relative sizes of each arc radius could vary. That is, their ratios could vary. In some embodiments, the ratio of the first arc radius to the second arc radius could vary in the range approximately between 1:2 and 9:10. In some embodiments, the ratio of the first arc radius to the second arc radius could be approximately 3:4. It may be appreciated that the ratio of the arc radii of the posterior and anterior ends may be suitably changed to accommodate different intended ranges of motion in different portions of the spine. For example, the ratio could have one value for implants used in the cervical spine and another ratio for implants used in the lumbar spine.

Additionally, the absolute sizes of each arc radius could vary in different embodiments. In some embodiments, the first arc radius could have a value approximately in the range between 4 and 6 centimeters. In one embodiment, the first arc radius could have a value of approximately 4.5 centimeters. In some embodiments, the second arc radius could have a value approximately in the range between 5 and 7 centimeters. In one embodiment, the first arc radius could have a value of approximately 6 centimeters. It may be appreciated that the absolute values of the arc radii of the posterior and anterior ends may be suitably changed to accommodate different intended ranges of motion in different portions of the spine. For example, the arc radii could have one set of value for implants used in the cervical spine and another set of values for implants used in the lumbar spine.

FIG. 8 is a schematic cross-sectional front view of core member 252. Visible within FIG. 8 is sagittal plane 702 (shown here as a line) and coronal plane 704. Sagittal plane 702 divides core member 252 into opposing lateral sides. Core member 252 further includes a first lateral portion 810 associated with a first lateral side and a second lateral portion 812 associated with a second lateral side.

As seen in FIG. 8 , curved engaging surface 262 includes a curved boundary 820 that lies within coronal plane 704. Curved boundary 820 has a substantially constant curvature. Specifically, curved boundary 820 has a substantially constant arc radius 830. This constant arc radius facilitates symmetric lateral bending on both sides of the body.

In some embodiments, arc radius 830 may be substantially smaller than first arc radius 730 and second arc radius 732 (see FIG. 7 ). In some embodiments, for example, the ratio of arc radius 830 to second arc radius 732 may be approximately 1:2. In some embodiments, arc radius 830 may have a value approximately in the range between 2 and 4 centimeters.

By using a core member with a curved engaging surface that has different arc radii in different regions, the implant described herein provides for natural motion between adjacent vertebrae. In particular, the embodiments described herein allow the top endplate to tilt and slide forwards along the core member during forward flexion. Additionally, the embodiments help limit the tilting and rearward motion of the top endplate along the core member during rearward extension.

In embodiments where the width of a core member varies between the posterior and anterior ends, the arc radius of the outer boundary of the curved engaging surface could vary. However, in other embodiments, the arc radius of the outer boundary of the curved engaging surface could be substantially constant from the posterior end to the lateral end.

FIG. 9 is a schematic top down view of core member 252 according to one embodiment. As seen in FIG. 9 , the width of core member 252 may vary between posterior portion 710 and anterior portion 712. For example, posterior portion 710 may have a maximum width 902 that tapers quickly towards a posterior edge 904. Moreover, the width of core member 252 tapers from maximum width 902 in the direction of anterior portion 712. For reference, an intermediate width 906 is shown for a portion of anterior portion 712. Here, intermediate width 906 is substantially less than maximum width 902. This tapered geometry may help control bending in the lateral direction and allow for some twisting between core member 252 and first endplate 220 (see FIG. 2 ). In other embodiments, however, core member 252 could have an approximately constant width.

The present embodiments provide an ADR device that facilitates both translation and rotation of the upper endplate relative to the lower endplate without requiring the use of a core that can slide relative to either of the endplates. Instead, the curvature of the core member (including posterior and anterior ends with different arc radii) allow the center axis of rotation of the upper endplate to translate along the core member. This translation is depicted schematically in, for example, FIGS. 10-13 below.

FIG. 10 is a schematic view of a patient 1000 who has a spinal implant. Adjacent to patient 1000 is an enlarged schematic view of spinal ADR device 1001 disposed between an upper vertebra 1030 and a lower vertebra 1032. Spinal ADR device 1001 further includes a first endplate 1002, a second endplate 1004, a core member 1006 and a matrix member 1008.

In FIG. 10 , patient 1000 is standing in a neutral position. In this position, first endplate 1002 is disposed in neutral position with a central axis 1003 of first endplate 1002 aligned with a reference axis 1040. In this position, core member 1006 and recess 1010 of first endplate 1002 are in contact along a first contact area 1050. To facilitate motion of first endplate 1002 along the curved engaging surface 1060 of core member 1006, recess 1010 may be shaped to accommodate the smallest area of curvature on core member 1006. To accomplish this, the arc radius associated with recess 1010 may match that of the arc radius of the anterior portion 1020 of core member 1006. In the neutral position, therefore, the larger curvature of posterior portion 1022 may prevent contact between curved engaging surface 1060 and recess 1010 at posterior portion 1022.

In FIG. 11 , patient 1000 tilts his head backwards, causing adjacent vertebrae in the cervical spine to undergo extension. Referring to FIG. 11 , as the cervical spine undergoes extension, first endplate 1002 is pushed backward and down the curved engaging surface 1060 until posterior portion 1022 of first endplate 1002 is engaged by matrix member 1008. In this position, core member 1006 and recess 1010 are in contact along a second contact area 1150.

Though matrix member 1008 may compress somewhat, depending on the amount of force applied by first end plate 1002, matrix member 1008 nonetheless acts to limit the rearward motion of first end plate 1002. Matrix member 1008 may also provide some cushioning and shock absorption following the initial contact between first end plate 1002 and matrix member 1008.

As seen in FIG. 11 , during extension, first endplate 1002 may not only tilt but may be translated in the posterior direction. Here, central axis 1030 has been translated in the posterior direction by a distance 1110 and has also rotated with respect to reference axis 1040. However, the variable curvature of core member 1006 is configured to allow for substantially more translation in the anterior direction than in the posterior direction, as described in further detail below. The result is that there is significantly less compression between the endplates at posterior portion 1022 during extension as there is between the endplates at anterior portion 1020 during flexion. This has the effect of limiting the relative translation between vertebrae during extension and, accordingly, how much the cervical spine can extend back.

In FIG. 12 , patient 1000 bends his neck forward, causing adjacent vertebrae in the cervical spine to undergo flexion. Referring to FIG. 12 , as the spine bends, first endplate 1002 is pushed forward and down the curved engaging surface 1060 until anterior portion 1020 first endplate 1002 is engaged by matrix member 1008.

In FIG. 12 , as patient 1000 continues pressing his neck down until his chin touches his chest, first endplate 1002 may slide further down curved engaging surface 1060. Additionally, matrix member 1008 may be compressed, further accommodating the forward translation of first endplate 1002 and decreasing the relative distance between the top of first endplate 1002 and the bottom of second endplate 1004 along the anterior side. In this position, core member 1006 and recess 1010 are in contact along a third contact area 1350. Because recess 1010 is sized to fit the larger arc radius of anterior portion 1020, third contact area 1350 may be substantially larger than, for example, the contact area 1050 when the device is in a neutral position (see FIG. 10 ).

As seen in FIGS. 12-13 , during flexion, first endplate 1002 may not only tilt but may be translated in the anterior direction. This can be seen clearly by comparing the position of central axis 1003 with reference axis 1040 (which represents the initial position of central axis 1003 in the neutral position). Here, central axis 1030 has been translated in the anterior direction by a distance 1203 (in FIG. 12 ) and by a distance 1303 (in FIG. 13 ). Additionally, in both FIGS. 12 and 13 , central axis 1030 has also rotated with respect to reference axis 1040. In this exemplary configuration, first endplate 1002 may be configured to translate by as much as 1 to 3 millimeters in the anterior direction. This allows the adjacent vertebrae to move as they normally would under flexion. While endplates in cervical devices may translate by as much as 1 to 3 millimeters, the amount of translation in a lumbar implant may be much more. For example, the endplate in a lumbar implant may translate up to approximately three times further than in the cervical region.

Using a configuration in which the upper endplate can not only tilt but also translate in the anterior direction relative to the lower endplate allows the adjacent vertebrae to achieve the necessary degree of compression so that a patient's neck can move through the entire range of normal motion, including putting his chin against his chest. Moreover, using a relatively less rigid matrix member provides shock absorption during flexion and prevents the upper endplate from coming into contact with the lower endplate. Thus, the present ADR device acts to provide an increased range of motion in the neck during flexion and a more limited range of motion in the next during extension, accommodating the natural motions of the neck.

FIG. 14 is a schematic front view of patient 1000 in a neutral position with an enlarged view of device 1001. As seen in FIG. 15 , as patient 1000 bends his neck laterally, first endplate 1002 travels down curved engaging surface 1060. During this motion, a central axis 1403 of first endplate 1002 travels laterally by a distance 1402 compared to a reference axis 1404. Because curved engaging surface 1060 has a smaller arc radius along its lateral sides than along its posterior or anterior sides, the degree of motion is more limited than during extension or flexion. Moreover, because curved engaging surface 1060 has a substantially constant arc radius, the degree of bending is equal on both sides.

As already described above, the embodiments not only control the motion of the upper endplate so as to mimic the natural motion of two adjacent vertebrae, but the presence of the softer matrix member substantially eliminates contact between the upper and lower endplates. Typically, endplates must be constructed from high strength materials such as metals that can withstand large contact forces as the endplates collide during flexion and/or extension. Since the current design eliminates contact between the endplates, the endplates can be manufactured from non-metallic materials. For example, in some embodiments, the endplates could be manufactured from plastic materials and/or ceramic materials that provide better biocompatibility with vertebra, improved wear characteristics and different degrees of strength compared to metal materials. Moreover, the use of non-metallic materials in the ADR device may substantially reduce or eliminate the metallic artifacts that may arise in MRIs when metallic prosthetics are present in the spine.

In different embodiments, the size and/or relative position of a dome on an upper endplate can vary. For example, FIGS. 16-18 depict three different embodiments in which the dome on the upper endplate varies in size and/or position. Different dome shapes and/or positions can be selected during surgery to facilitate better connection with the upper vertebra. Specifically, the dome may be better aligned and may fit better with the natural shape of the inferior side of the vertebra.

In FIG. 16 , upper endplate 1602 is configured with a dome 1604 that is substantially centered along the endplate. Such a configuration may be most useful for engaging the inferior side 1610 of a vertebra 1612 with a centrally located concave region 1614. In FIG. 17 , upper endplate 1702 is configured with a dome 1704 that is disposed closer to posterior end 1706 of upper endplate 1702. Such a configuration may be most useful for engaging the inferior side 1710 of a vertebra 1712 with a posteriorly located concave region 1714. In FIG. 18 , upper endplate 1802 is configured with a substantially flatter dome 1804 compared to dome 1604 and dome 1704. For example, dome 1804 may have a height 1820 compared to a substantially larger height 1620 for dome 1604. Such a configuration may be most useful for engaging the inferior side 1810 of a vertebra 1812 with a relatively shallow concave area 1814.

Embodiments can include additional provisions to prevent contact between opposing endplates in an ADR device. In some embodiments, a matrix member can be shaped to extend radially outward over the lower endplate so that no portion of the lower endplate is exposed on a superior side.

FIG. 19 depicts an alternative embodiment of part of an ADR device 1900 that includes a core member 1902, a matrix member 1904, an upper endplate 1908 and a lower endplate 1910. As seen in FIG. 19 , matrix member 1904 includes a peripheral portion 1920 that extends over a peripheral lip 1912 of lower endplate 1910. Using this configuration, matrix member 1904 completely covers the superior side of lower endplate 1910 and prevents any contact between lower endplate 1910 and upper endplate 1908.

The exemplary ADR device can be implanted into a patient's spine using a suitable surgical method. In some embodiments, after removing some or all of the tissue between adjacent vertebrae, a surgeon may first implant the upper and lower endplates. For example, the surgeon may place the lower endplate against one vertebra. In cases where the lower endplate includes teeth or similar provisions, the surgeon may apply pressure and/or tap the endplate to that the teeth engage the vertebra and prevent the lower endplate from moving with respect to the vertebra. The upper endplate may also be placed against the opposing vertebra. Specifically, an upper endplate with a suitable dome for engaging a concave area in the vertebra can be selected. As described above, a surgeon could choose from at least endplates with domes that are either centrally or posteriorly located. Also, a surgeon could choose from at least endplates with domes that have different overall heights. Once a suitable endplate has been selected, the endplate can be inserted and placed against the vertebra so that the dome engages the concave area of vertebra.

Once the endplates have been positioned and/or fixed in place, a surgeon may insert a core assembly comprising both a core member and a matrix member. To insert the core assembly, the surgeon can insert the matrix member into a corresponding recess of the lower endplate while simultaneously inserting a portion of the core member into a corresponding recess of the upper endplate. Once the core member has been inserted, the compressive forces of the spine may act to keep the matrix member fixed in the recess of the lower endplate and the core member engaged with the recess of the upper endplate.

FIG. 20 is a schematic perspective lateral view of a portion of a spine and two endplates of an artificial disc replacement device being inserted into the disc space between two vertebrae. FIG. 20 shows a portion of a spinal column 2000. In order to implant an artificial disc replacement device, the method of implantation includes removing a natural spinal disc from between a first vertebra 2005 and a second vertebra 2010, thereby forming a disc space between first vertebra 2005 and second vertebra 2010. Because the disclosed ADR device is modular, the endplates can be inserted into the disc space without the core assembly installed. For example, as shown in FIG. 20 , a first device endplate 2015 and a second device endplate 2020 can be inserted into the disc space. Because there is no core assembly present between the endplates, the overall profile (height) of the two endplates together is significantly less than the fully assembled implant. Accordingly, the endplates by themselves can be easily inserted into the disc space without the need for distraction of the vertebrae.

FIG. 21 is a schematic view of the spine shown in FIG. 20 with the device endplates inserted into the disc space. As shown in FIG. 21 , first endplate 2015 and second endplate 2020 easily fit into the disc space between first vertebra 2005 and second vertebra 2010.

Once the endplates are inserted into the disc space, a distraction tool may be used to distract the endplates and seat them against the opposing vertebrae.

FIG. 22 is a schematic view of the spine shown in FIG. 20 with the device endplates being distracted by a distraction tool. As shown in FIG. 22 , a distraction tool 2200 may be used to distract the endplates. For example, as shown in FIG. 22 , compressing a handle portion of distraction tool 2200 (illustrated by arrows 2205) may create distractive force (illustrated by arrows 2210), which may seat first endplate 2015 against first vertebrae 2005 and seat second endplate 2020 against second vertebrae 2010.

Once the endplates are seated against the vertebra, an x-ray may be performed in order to evaluate the placement of the first endplate and the second endplate within the disc space.

FIG. 23 is a schematic view of the spine shown in FIG. 20 with the endplates seated and the patient undergoing an x-ray. As shown in FIG. 23 , an x-ray machine 2300 may be utilized for imaging the spine with the endplates seated therein. FIG. 23 illustrates x-ray machine 2300 taking an anterior-posterior view of the spine. The method may also include taking one or more lateral views and/or one or more views taken at an oblique angle.

If the imaging reveals that the ADR device is not placed to the satisfaction of the surgeon, or if the surgeon otherwise wants to relocate the device, the endplates may be removed and/or repositioned.

FIG. 24 is a schematic view of the spine shown in FIG. 20 with the endplates being withdrawn from the disc space. As shown by an arrow 2400 in FIG. 24 , first endplate 2015 and second endplate 2020 may be removed from the disc space. If the endplates have already been seated against the vertebrae, a distraction tool may be used to unseat first endplate 2015 from first vertebra 2005 and to unseat second endplate 2020 from second vertebra 2010.

With the endplates now unseated, the endplates may be repositioned within the disc space. In some cases, the endplates may be individually positioned within the disc space.

FIG. 25 is a schematic view of the spine shown in FIG. 20 with the endplates being repositioned within the disc space. As shown in FIG. 25 , the method of implantation may include relocating first endplate 2015 or second endplate 2020 within the disc space. A first arrow 2500 indicates the direction of reinsertion of the endplates. Arrows 2505 illustrate the lateral mobility with which the endplates may be adjusted in order to reposition the endplates.

With the endplates repositioned, they may be distracted again in order to seat them against the vertebrae. FIG. 26 is a schematic view of the spine shown in FIG. 20 with the endplates once again being distracted, as illustrated by arrows 2600.

Once the endplates are repositioned, the spine may be x-rayed again in order to confirm the positioning is as desired. If the positioning is to the surgeon's liking, the core assembly may be inserted.

FIG. 27 is a schematic view of the spine shown in FIG. 20 with the endplates distracted and an implant core assembly being inserted between the endplates. As shown in FIG. 27 , an ADR core assembly 2700 may include two components, as discussed above. In particular, core assembly 2700 may include a core member 2705 and a matrix member 2710. It will be understood that first endplate 2015, second endplate 2020, core member 2705, and matrix member 2710 may include any of the features described above and shown in the accompanying figures.

As shown by an arrow 2715 in FIG. 27 , core assembly 2700 may be inserted between first endplate 2015 and second endplate 2020. In some cases, core assembly 2700 may be inserted between the endplates without the need for distraction of the endplates. In some cases, only minimal distraction (e.g., approximately 1-2 mm) may be required. Because core assembly 2700 can be inserted without little to no distraction of the endplates, there need not be any significant impact made on core assembly 2700. That is, the core assembly may be simply pushed in with the fingers or, if a mallet is used, the core assembly may be inserted using only the lightest taps from the mallet.

FIG. 28 is a schematic view of the spine shown in FIG. 20 with core assembly 2700 positioned between first endplate 2015 and second endplate 2020. FIG. 29 is a schematic view of spine 2000 with the distraction removed and spine 2000 allowed to return into compression as indicated by arrows 2900.

FIGS. 30-33 illustrate a similar procedure from a lateral view. As discussed below, the ADR device may include one or more teeth, which may lock in the positioning of the endplates. Accordingly, seating the first endplate against the first vertebra may include inserting the one or more teeth into the first vertebra. Similarly, seating the second endplate against the second vertebra may include inserting the one or more teeth into the second vertebra.

In some cases, when seating the endplates prior to the x-ray, the teeth may be completely countersunk into the bone of the vertebrae. In other cases, the teeth may initially be only partially inserted into the bone. The partial insertion into the bone enables the endplates to be removed and repositioned easily. However, even if the teeth are fully countersunk into the bone, removal and repositioning of the endplates can still be accomplished using a distraction tool. In this case, the holes left by the initial positions of the teeth may provide a benefit of promoting bone growth.

FIG. 30 is a schematic side view of a spine with endplates of an artificial disc replacement device being inserted between vertebrae of the spine. As shown in FIG. 30 , first endplate 2015 and second endplate 2020 are inserted into the disc space, as illustrated by an arrow 3000. The upper vertebral endplate 3020 and the lower vertebral endplate 3030 may be prepared for mating with the device endplates. For example, as shown in FIG. 30 , a recess 3025 in upper vertebral endplate 3020 may be fashioned, in order to receive a protrusion 3005 on first endplate 2015.

FIG. 30 also shows first endplate 2015 having upper teeth 3010, which may embed into upper vertebral endplate 3020 upon distraction of the endplates. Similarly, second endplate 2020 may have lower teeth 3015, which may embed into lower vertebral endplate 3030 upon distraction of the endplates.

FIG. 31 is a schematic side view of the spine shown in FIG. 30 with the endplates being distracted by a distraction tool. As shown in FIG. 31 , distraction tool 2200 may be used, e.g., by exerting a force (shown by arrow 3100) on the handle in order to produce a distraction force (shown by arrow 3105). This distraction force may seat first endplate 2015 against upper vertebral endplate 3020. This distraction force may also seat second endplate 2020 against lower vertebral endplate 3030. As further shown in FIG. 31 , with the endplates seated, upper teeth 3010 and lower teeth 3015 may be embedded in the bone.

FIG. 32 is a schematic side view of the spine shown in FIG. 30 with the endplates distracted and an implant core assembly being inserted between the endplates. As shown in FIG. 32 , core assembly 2700 may be inserted (as shown by an arrow 3200) in between first endplate 2015 and second endplate 2020. To facilitate this insertion, a distraction force (illustrated by arrows 3205) may be imparted on the endplates. It will be noted that, in some embodiments, the distraction may be performed such that the vertebra are separated in lordosis. Not only is lordosis the natural condition of the spine in the cervical and lumbar regions, but also the lordotic angle enables the core assembly to be inserted more easily, because it opens the anterior portion of the spine more than the posterior portion of the spine, like a clamshell.

FIG. 33 is a schematic side view of the spine shown in FIG. 30 with the distraction removed and the spine allowed to return into compression, as illustrated by arrows 3300.

FIG. 34 is a flowchart illustrating steps of a method of implanting an artificial disc replacement device according to an embodiment. As shown in FIG. 34 , the method may first include removing the natural disc of the patient. (Step 3400.) Then, at step 3405, the method may include fashioning the vertebral endplates. This includes the process by which the bone surfaces of the vertebral endplates are prepared to receive the implant.

At step 3410, the method includes inserting the implant endplates into the disc space. Once the endplates are inserted into the disc space, the endplates may be distracted in order to seat the implant endplates against the vertebral endplates. (Step 3415.)

With the endplates seated, an x-ray may be taken (step 3420) in order to verify the positioning of the endplates. The method then involves a decision as to whether the endplates are positioned to the surgeon's liking. (Step 3425.) If yes, then the method proceeds to inserting the core assembly of the implant. (Step 3430.) If not, then the implant endplates may be repositioned. (Step 3435.) Once the endplates have been repositioned, another x-ray may be taken (step 3420), and so forth.

While various embodiments have been described, the description is intended to be exemplary, rather than limiting, and it will be apparent to those of ordinary skill in the art that many more embodiments and implementations are possible that are within the scope of the embodiments. Although many possible combinations of features are shown in the accompanying figures and discussed in this detailed description, many other combinations of the disclosed features are possible. Any feature of any embodiment may be used in combination with, or substituted for, any other feature or element in any other embodiment unless specifically restricted. Therefore, it will be understood that any of the features shown and/or discussed in the present disclosure may be implemented together in any suitable combination. Accordingly, the embodiments are not to be restricted except in light of the attached claims and their equivalents. Also, various modifications and changes may be made within the scope of the attached claims. 

What is claimed is:
 1. A method of implanting an artificial disc replacement device, comprising: removing a natural spinal disc from between a first vertebra and a second vertebra, thereby forming a disc space between the first vertebra and the second vertebra; inserting a first endplate and a second endplate of the artificial disc replacement device into the disc space; using a distraction tool to distract the first endplate and the second endplate in order to seat the first endplate against the first vertebrae and to seat the second endplate against the second vertebrae; performing an x-ray to evaluate the placement of the first endplate and the second endplate within the disc space; using the distraction tool to unseat the first endplate from the first vertebra and to unseat the second endplate from the second vertebra; repositioning the first endplate or the second endplate within the disc space; and subsequently, inserting a core assembly of the artificial disc replacement device between the first endplate and the second endplate.
 2. The method of claim 1, wherein the core assembly includes a core member and a matrix member, wherein the core member includes a base portion and a curved engaging surface, and wherein the base portion of the core member is embedded in the matrix member.
 3. The method of claim 2, wherein the first endplate includes a first recess for receiving the curved engaging portion of the core member; and wherein the second endplate includes a second recess for receiving the matrix member.
 4. The method of claim 3, wherein: the core member includes a sagittal plane that separates the core member into a first lateral side and a second lateral side; the core member also including a coronal plane that separates the core member into an anterior side and a posterior side; wherein the curved engaging surface includes a curved boundary that extends within a first plane that is parallel with the sagittal plane; wherein the curved boundary has a first arc radius along an anterior portion disposed on the anterior side of the core member; and wherein the curved boundary has a second arc radius along a posterior portion disposed on the posterior side of the curved boundary, wherein the second arc radius is substantially different from the first arc radius.
 5. The method of claim 3, wherein the matrix member is substantially more compressible than the core member.
 6. The method of claim 1, wherein the first endplate includes one or more teeth; and wherein seating the first endplate against the first vertebra includes inserting the one or more teeth into the first vertebra.
 7. The method of claim 1, wherein the second endplate includes one or more teeth; and wherein seating the second endplate against the second vertebra includes inserting the one or more teeth into the second vertebra.
 8. A method of implanting an artificial disc replacement device, comprising: inserting a first endplate and a second endplate of the artificial disc replacement device into a disc space between a first vertebra and a second vertebra; using a distraction tool to distract the first endplate and the second endplate, thereby placing the first endplate against the first vertebra and placing the second endplate against the second vertebra; performing an x-ray to evaluate the placement of the first endplate and the second endplate within the disc space; using the distraction tool to reposition at least one of the first endplate and the second endplate within the disc space; and subsequently, inserting a core assembly of the artificial disc replacement device between the first endplate and the second endplate.
 9. The method of claim 8, wherein the core assembly includes a core member and a matrix member, wherein the core member includes a base portion and a curved engaging surface, and wherein the base portion of the core member is embedded in the matrix member.
 10. The method of claim 9, wherein the first endplate includes a first recess for receiving the curved engaging portion of the core member; and wherein the second endplate includes a second recess for receiving the matrix member.
 11. The method of claim 10, wherein: the core member includes a sagittal plane that separates the core member into a first lateral side and a second lateral side; the core member also including a coronal plane that separates the core member into an anterior side and a posterior side; wherein the curved engaging surface includes a curved boundary that extends within a first plane that is parallel with the sagittal plane; wherein the curved boundary has a first arc radius along an anterior portion disposed on the anterior side of the core member; and wherein the curved boundary has a second arc radius along a posterior portion disposed on the posterior side of the curved boundary, wherein the second arc radius is substantially different from the first arc radius.
 12. The method of claim 11, wherein the curved engaging surface includes a second curved boundary that extends within a second plane that is parallel with the coronal plane; wherein the second curved boundary has a third arc radius that is substantially constant.
 13. The method of claim 12, wherein the third arc radius is substantially smaller than the first arc radius.
 14. The method of claim 10, wherein the matrix member is substantially more compressible than the core member.
 15. A method of implanting an artificial disc replacement device, comprising: inserting a first endplate and a second endplate of the artificial disc replacement device into a disc space between a first vertebra and a second vertebra; using a distraction tool to distract the first endplate and the second endplate, thereby placing the first endplate against the first vertebra and placing the second endplate against the second vertebra; using the distraction tool to reposition at least one of the first endplate and the second endplate within the disc space; and subsequently, inserting a core assembly of the artificial disc replacement device between the first endplate and the second endplate.
 16. The method of claim 15, wherein the core assembly includes a core member and a matrix member; wherein the first endplate includes a recess and wherein the core member includes a curved engaging surface in continuous contact with the recess, and wherein the first endplate can move along the curved engaging surface.
 17. The method of claim 16, wherein the matrix member is disposed between the core member and the second endplate and prevents contact between the core member and the second endplate; wherein the matrix member is positioned to prevent the first endplate from contacting the second endplate as the first endplate moves along the core member.
 18. The method of claim 17, wherein the second endplate includes a second recess that receives the matrix member.
 19. The method of claim 18, wherein a superior surface of the matrix member is raised above a superior surface of the second endplate.
 20. The method of claim 19, wherein the second endplate includes a lip that surrounds the second recess and wherein the matrix member includes a peripheral portion that covers the lip. 